Toxoplasma gondii is an intracellular protozoan parasite that is the causative agent of Toxoplasmosis. Toxoplasma infection in mice provides an excellent experimental model for understanding food borne infections and chronic infections of the brain. The overall goal of this project is to gain a deeper understanding of how the mammalian immune system responds to chronic Toxoplasma infection by tracking parasites and immune cells in the brain. Specifically, we propose to examine how T cell interactions with parasites and invaded host cells changes during progressing versus controlled chronic infection (Aim 1), to investigate the key features that distinguish a protective CD8 T cell response from a non-protective one (Aim 2), and to investigate the role of regulatory T cells in modulating T cell effectors responses (Aim 3). PUBLIC HEALTH RELEVANCE: Toxoplasma gondii is a parasite that causes birth defects or brain infection in immune compromised adults. We are using a mouse infection model and advanced microscopy methods to gain a better understanding of how the immune system protects against the parasite and how the parasite attempts to evade the immune system. Because Toxoplasma establishes life-long infection of the brain, these studies have relevance for the development of therapeutic strategies to treat infections of the brain and chronic infections.